You can get a quick summary of this book on p 135 or 326. If you are not up to speed on evolutionary psychology, you should first read one of the numerous recent texts with this term in the title. One of the best is "The Handbook of Evolutionary Psychology" 2nd ed by Buss. Until about 15 years ago, ´explanations´ of behavior have not really been explanations of mental processes at all, but rather vague and largely useless descriptions of what people did and what they said, with no insight into why. We might say that people gather to commemorate an event, praise god, receive his (or her or their) blessings, etc., but none of this describes the relevant mental processes, so we might say they are explanations in much the same way that it explains why an apple drops to the ground if we say its because we released it, and it's heavy-there is no mechanism and no explanatory or predictive power. This book continues the elucidation of the genetic basis of human behavior which has been almost universally ignored and denied by academia, religion, politics and the public (see Pinker´s excellent book ``The Blank Slatè`). His statement (p3) that it is meaningless to ask if religion is genetic is mistaken as the percentage of variation of any behavior due to genes and environment can be studied, just as they are for all other behaviors (see e.g., Pinker). The title should be Preliminary Attempts to Explain Some Aspects of Primitive Religion, since he does not treat higher consciousness at all (e.g., satori, enlightenment etc.) which are by far the most interesting phenomena and the only part of religion of personal interest to intelligent, educated people in the 21st century. Reading this entire book, you would never guess such things exist. Likewise, for the immense field of drugs and religion. It lacks a framework for rationality and does not mention the dual systems of thought view which is now so productive. For this I suggest my own recent papers. Nevertheless, the book has much of interest, and in spite of being dated is still worth reading.
Those wishing a comprehensive up to date framework for human behavior from the modern two systems view may consult my book ‘The Logical Structure of Philosophy, Psychology, Mind and Language in Ludwig Wittgenstein and John Searle’ 2nd ed (2019). Those interested in more of my writings may see ‘Talking Monkeys--Philosophy, Psychology, Science, Religion and Politics on a Doomed Planet--Articles and Reviews 2006-2019 3rd ed (2019), The Logical Structure of Human Behavior (2019), and Suicidal Utopian Delusions in the 21st Century 4th ed (2019)